Radial piston pump

ABSTRACT

A radial piston pump of the type, in which an excentric rotor (7) is adapted to cause the pistons (4) to perform a reciprocating movement within radial cylinders (3) in the pump body (1), the radial inner ends of the pistons (4) being each provided with a broadened foot (6), said broadened feet (65) being kept in contact with the rotor (7) also during the suction strokes of the respective pistons (4) by means of a coupling ring (26) of a substantially L-shaped cross section, the axial ring portion (26a) of which engages the radial outer end faces of the broadened feet (6) and the radial portion (26b) of which keeps said ring (26) axially in place. According to the invention the coupling ring (26) has its radial portion (26b) bearing loosely against a radial sliding surface, while the broadened feet (6) at the radial inner piston ends are in the shape of heads which are integrally formed with the respective pistons (4), the free end faces of said heads, as well as the end faces adjoining the respective pistons (4) being spherically shaped, the axial portion of the coupling (26) having an inner circumferential surface of a slightly conically widening shape.

FIELD OF THE INVENTION

The invention relates to a radial piston pump of the type, in which aneccentric rotor is adapted to cause the pistons to perform areciprocating movement within radial cylinders in the pump body, theradial inner ends of the pistons being each provided with a broadenedfoot, said broadened feet being kept in contact with the rotor alsoduring the suction strokes of the respective pistons by means of acoupling ring of a substantially L-shaped cross-section, the axial ringportion of which engages the radial outer end faces of the broadenedfeet and the radial portion of which keeps said ring axially in place.

Discussion of the Prior Art

Such a pump is known from German Offenlengungsschrift 1.928.853.

With this well-known pump the broadened feet at the radial inner pistonends are formed by sliding shoes which are pivotally connected to therespective piston ends. The effective sliding surfaces of said slidingshoes are shaped to conform with the cylindrical surface of the rotorand the cylindrical inner circumferential surface of the axial ringportion of the coupling ring respectively. The coupling ring has itsradial portion fixedly connected to the rotor. The sliding shoes, whichare stationary as seen in the direction of rotation, are thus slidinglyguided with an inner and an outer cylindrical sliding surface betweentwo concentric cylindrical surface portions of the rotor and of thecoupling ring respectively. This means, that a considerable frictionalresistance has to be overcome, said frictional resistance being furtherincreased by the friction in the pivot connection between the pistonsand the sliding shoes.

SUMMARY OF THE INVENTION

The invention therefore aims at providing a pump of the above type, withwhich the frictional resistance to be overcome in operation, issubstantially reduced.

According to the invention this aim is achieved in that the couplingring has its radial portion bearing loosely against a radial slidingsurface, while the broadened feet at the radial inner piston ends are inthe shape of heads which are integrally formed with the respectivepistons, the free end faces of said heads, as well as the end facesadjoining the respective pistons being spherically shaped, the axialportion of the coupling having an inner circumferential surface of aslightly conically widening shape.

Due to the measures according to the invention the areas of contactbetween the mutual sliding surfaces of the pistons, the coupling ringand the rotor are substantially reduced to point and line contacts,whereas the movements of the coupling ring will in practise be limitedto a translational movement of a small amplitude relative to thestationary radial sliding surface. Moreover, the end faces of the pistonheads adjoining the pistons may rock on the inner circumferentialsurface of the axial portion of the coupling ring.

The omission of a pivot connection between the pistons and the heads ofthe same not only avoids the friction involved with such pivotconnection but also leads to a simpler construction.

It is to be noted, that German Offenlegungsschrift 1.653.643 discloses aradial piston pump, wherein the radial inner piston ends are alsoprovided with an intergrally formed widened head, the free end face ofwhich is of a spherical shape. With this embodiment, however, theannular end faces adjoining the respective pistons are flat in shape,while the coupling ring has at its inner circumference an arcuateportion (turned with its convex side towards the axis of the pump) atthe location of each piston head, said arcuate portions engaging theflat annular end faces of the respective piston heads.

A disadvantage of this well-known construction is that the coupling ringmay, in addition to the required translational movement, easily make anundesired rotational movement relative to the pistons, as a result ofwhich the widened heads may get jammed between rotor and coupling ring.

The invention will be hereinafter further described by way of examplewith reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an axial cross-sectional view through a radial piston pumpaccording to the invention, as seen along the line I--I in FIG. 2;

FIG. 2 represents a cross-section along the line II--II in FIG. 1 and

FIG. 3 is an enlarged longitudinal cross-sectional view through the leftlower part of the device of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The annular pump body 1 is surrounded by an annular wall member 2 andhas a number of radially directed pumping cylinders 3, in which pistons4 are mounted for a reciprocating movement.

The pump body 1 confines a central space 5, into which the radial innerends project and which also accommodates the eccentric part 8 of therotor 7; the radial inner piston ends broaden into heads 6. One end(i.e. the left end as seen in FIG. 1) of the central space 5 (FIG. 3) isclosed by a cover 10 and at a distance from the latter within the pumpbody 1 ball bearings 11 and 12 are provided, in which the centricportion 9, 9a of the rotor 7 is journalled.

13 designates a connection shaft, made e.g. of a suitable artificialresin, one end of which non-rotatably engages a central bore 14 in thecentrical portion 9 of the rotor 7 and the other end of whichnon-rotatably engages the drive shaft 15 of the pump engine (electricmotor) 16.

The space between the pump body 1 and the housing of the electric motor16 is radially outwardly confined by a shell 17, which is an extensionof the annular wall member 2 and constitutes the outer wall of areservoir 18 for the liquid to be pumped. Liquid may flow from thereservoir 18 through a filter 19 into a suction passage 30 and throughsuction openings 20 into each of the cylinders 3; the suction passage 30is constituted by a circumferential groove of a relatively large depth.

The radial outer ends of the cylinders 3 merge into a circumferentialpassage 21 that is provided in the outer wall of the pump body 1. Theconnecting openings between the cylinders 3 and the circumferentialpassage 21 are broadened into chambers 22 for disc-shaped pressurevalves 23. The pressure valves 23 are pressed on their seats by means ofa common resilient closure element, that is received within thecircumferential passage 21 and is constituted by a tangentiallypre-stressed O-ring 24; the tangential pre-tension of the ring 24produces a radially inwardly directed closing force on each of thepressure valves 23.

The circumferential passage 21 is radially outwardly closed by anannular member 31 of plastics material, having at its circumferentialinner surface a groove for receiving the O-ring 24; a radially directedconnecting passage 28 (FIG. 2), which may be selected ratherarbitrarily, connects the circumferential passage 21 to a connection 29for a pressure line that is provided on the end wall of the pump body 1.

The effective outer circumferential portion of the eccentric rotor part8 is formed by a slide bearing ring 25 mounted on said rotor part. Whilethe rotor 7 is rotating the slide bearing ring 25 will remain stationaryrelative to the eccentric rotor part 8, so that it will merely perform atranslational movement relative to the pump body 1.

The pistons have their radial inner ends 6 engaging the ring 25 and arecaused by the rotating rotor 7 to reciprocate within the respectivecylinders. Each time the rotor will cause a piston to move radiallyoutwardly so as to perform a pressure stroke, whereby the respectivepressure valve 23 is lifted from its seat against the radially inwardlydirected closure force of the O-ring 24, while another piston isperforming an inwardly directed suction stroke so as to extract liquid(e.g. hydraulic fluid) from the reservoir 18 through the respectivesuction opening 20 via the suction passage 30 and the filter 19 (whilethe respective pressure valve is kept closed).

To perform a suction stroke the pistons will have to follow theeccentric rotor part 8, which means that the contact between the radialinner piston ends and the rotor part 8 (i.e. the slide bearing ring 25)must be maintained. In accordance with the present invention this isachieved in a simple and effective manner by means of a loosely mountedcoupling ring 26.

An axially directed ring portion 26a of the coupling ring 26 engages theoutwardly facing end faces of the heads 6 and thereby keeps said headsin contact with the ring 25 of the eccentric rotor part 8. An annulardisc portion 26b is connected with the ring portion 26a and ispositioned in a plane at right angles to the pump axis; this annulardisc portion 26b is loosely positioned between the right- and end face(as seen in the drawing) of the slide bearing ring 25 and the oppositeend face 27 of the pump body 1 or a filling ring 27a lying flushtherewith respectively. The coupling ring 26, which may be formed of asuitable artificial resin, is coaxially positioned relative to theeccentric rotor part 8 and is performing, in operation, a translationalmovement together with the slide bearing ring 25 relative to thestationary pump body 1.

The coupling ring 26 could also be mounted on the opposite side of thebearing 25. In that case the annular disc portion 26b would becomeloosely positioned between the left end surface of the slide bearingring 25 and the inner side of the cover 10.

We claim:
 1. A radial piston pump of the type in which an eccentricrotor is adapted to cause pistons to perform a reciprocating movementwithin radial cylinders in a pump body, radial inner ends of saidpistons being each provided with a broadened foot, said broadened feetbeing kept in contact with said rotor also during suction strokes ofsaid respective pistons by means of a coupling ring of a substantiallyL-shaped cross-section, said coupling ring having an axial ring portionwhich engages radial outer end faces of said broadened feet and having aradial portion which keeps said ring axially in place, characterized inthat said radial portion of said coupling ring bears loosely against aradial sliding surface, and said broadened feet at said radial innerpiston ends are in the shape of heads which are integrally formed withthe respective pistons, free end faces of said heads and end faces ofsaid heads adjoining the respective pistons being spherically shaped,and an axial portion of said coupling ring having an innercircumferential surface of a slightly conically widening shape.